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Re: [TCML] VTTC-tuning. John got me started ;-)



Dex Dexter wrote:
I  measured nothing.
Ok. Then di/dt is based on some predictions? You stated that it works out near to DC's equation, so I assumed you had made a measurement.
And even if I measure current ,how to measure top volts to determine what efficiency factors enter the formula?
Difficult for a direct measurement. DC Cox does have a method which he uses for approximation, but I have not tried it myself. Unfortunately, I don't remember the details and can't find any info about it on my pc.

How did you and others found factor of 0.7 for a typical spark gap tesla coil?
DC I expect is looking at the equation V = Vp*sqrt(Ls/Lp) and comparing those results to his measured approximations and inserting the efficiency factor of 0.7 as an average over whatever series of measurements were made (and this is only an assumption on my part). As you know, losses are not part of the equation but they exist.

For Lp, the inductance at low frequency is fine. For the secondary, it would be more accurate to insert the high frequency inductance. In many coils, it's not a large change, but there are geometries where the distance between the two do become significant. As long as you always use the high frequency inductance, then your good for all geometries. As you know, the top terminal affects the peak potential due to breakout. Note that this equation or anything similar will never account for the top terminal geometry and the surface field developed due to the charge and where corona inception occurs followed by breakout. This is a physical limitation that should also be accounted for, but until we can directly measure the top voltage at the terminal of a Tesla coil with accuracy, then we can only make educated guesses.

Take care,
Bart


Dex
--- bartb@xxxxxxxxxxxxxxxx wrote:

From: bartb <bartb@xxxxxxxxxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Cc:
Subject: Re: [TCML] VTTC-tuning. John got me started ;-)
Date: Wed, 08 Apr 2009 19:00:50 -0700

Hi Dex,

Moderators are not going to change an equation. They may later reply and correct it with a reply, but they don't need to be messing with a persons equation (what is obvious is subjective to how much attention is being paid to the equation). Their looking for more of content as it relates to the TCML and not necessarily every calculation detail.

DC's equation as you state is a standard energy equation that has been around forever. What DC is doing is showing are losses with the efficiency factor of 0.7. The same equation is derived with the capacitances as well. Your equation is dependent on di/dt. Have you measured this yet? If yes, what was the change in current and over what time frame (0 to peak). May as well state L also. This equation requires measurement to verify, so I can't go any further without some data if you have it.

Take care,
Bart



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